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5.6 Systems with complex background contributions

gregates may be suggested [121]. A protolysis term also exists in the spectrum of the mixture of noncritical composition (x = 0.148,τ1 = 2.7ns, A1 = 2.1·10−3, 25oC), shown in Fig.(5.27).

Figure 5.27: Ultrasonic excess attenuation spectrum for 2,6- dimethylpyridine-water mixture of noncritical composition Y = 0.148 at 25 oC.

Dielectric and ultrasonic relaxation measure- ment as well as depolarized Rayleigh scatter- ing and nmr studies reported in [118], [119], [120], have supported the idea of 2,6-DMP aggregates including water. In the previous treatment of (2,6-DMP-H2O) spectra [120] two Debye-type relaxation terms have been con- sidered in addition to the critical contribution. The recent evaluation proved one noncritical relaxation term RD(f) to be sufficient for an adequate representation of the experimental data Fig.(5.28), which likely reflects the pro- tolysis equilibrium Eq.(5.19). Hence, at least two relaxation terms,

are required for an adequate analytical representation of the experimental data [123]. An-

Figure 5.28: Excess-attenuation-per-wavelength spectrum for the 2,6-dimethylpyridine- water mixture of critical composition at 30 oC. Dashed and dotted lines are graphs of the critical Rc(f) and noncritical terms RD(f), respectively, in the spectrum Eq.(5.20). The full line shows the sum of these terms.

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